1. Field
The disclosed and claimed concept relates generally to handheld electronic devices and, more particularly, to handheld electronic devices including a flash device and a battery. The disclosed and claimed concept also relates to methods of driving a flash device of a handheld electronic device including a battery.
2. Description of the Related Art
Numerous types of handheld electronic devices are known. Examples of such handheld electronic devices include, for instance, personal data assistants (PDAs), handheld computers, two-way pagers, cellular telephones, e-mail devices and the like. Such handheld electronic devices are generally intended to be portable and thus are small and battery powered. While some handheld electronic devices include a wireless communication capability, other handheld electronic devices are standalone devices that do not communicate with other devices.
Some handheld electronic devices include a camera and a light emitting diode (LED) camera flash, and are powered by a single lithium ion battery. The current drawn from operating the LED camera flash is relatively very large (e.g., without limitation, up to about 1.2 A; any suitable value) for a relatively long period of time (e.g., without limitation, up to about 80 mS; up to about 250 mS; any suitable value) and can easily brown-out the device under certain conditions. Brown-out is also known as battery droop and means that the battery voltage drops to a level that can impair the operation of other device functions, possibly even causing the device to reset. A lithium ion battery's ability to maintain its voltage is dependent upon various factors, such as the age of the battery and its temperature (i.e., the equivalent series resistance (ESR) of the battery varies with these parameters). For example, when the battery voltage is low or if the battery is cold, then the battery ESR may be too high to support a camera flash. In such cases, the battery droop may trip battery supervisory circuits, causing the device to reset or go into a sleep mode. This can be a frustrating experience for the user.
U.S. Patent Application Pub. No. 2008/0037979 discloses in its Background section that one approach to try and address the problem of battery droop is to map known levels of battery capacity and voltage into tables that are associated with events that should occur at those battery capacity levels. This can be an effective approach for components that draw relatively small or steady amounts of power. However, for a flash or other high-intensity component, a large margin of battery reserve is needed as the momentary conditions of a battery that can withstand such a high-intensity burst can vary.
Publication 2008/0037979 further discloses an electronic device in which the battery level is measured, a determination is made if the battery level exceeds a predetermined threshold, and, if not, then a flash photograph is not permitted. Otherwise, if the battery level exceeds the predetermined threshold, then flash settings are adjusted to reduce power consumption by the flash so as to not cause a supervisory circuit to shut down the device. The exact settings for the flash can be chosen so as to maximize the amount of light output from the flash, but without tripping the supervisor circuit. Numerous profiles or representations thereof can be gathered for different start voltages of the battery and different ambient temperatures. An average version of the profiles can be established by determining profiles for a number of substantially identical copies of the device, so that variability, between devices can be ascertained and considered when establishing profiles.
U.S. Patent Application Pub. No. 2008/0014997 discloses a battery-powered communications device including a slump monitoring system, which monitors the battery voltage. The slump monitoring system determines if the monitored value is below a predetermined threshold. The predetermined threshold may be a dynamic parameter that depends on the transmit power level required for a given transmission. If the value is below the predetermined threshold, then the slump monitoring system sends an interrupt signal to terminate the transmission, which causes a transmitter to be powered down. If the monitored value is above the predetermined threshold, then the slump monitoring system continues to monitor. The slump monitoring system can include an analog to digital converter (ADC), a trigger input, a trigger delay, one or more analog inputs, a control/math block, and one or more outputs. The one or more analog inputs receive one or more signals related to battery voltage level or temperature and provide these signals to the ADC.
Some prior proposals use a pre-flash function to determine the ESR of the battery. U.S. Patent Application Pub. No. 2008/0164847 discloses a method and apparatus for maintaining a maximum sustained flash current over the whole length of a flash using a programmable current drive in a handheld portable device powered by a battery. The method measures the battery voltage before and after a flash is initiated and calculates the ESR of the battery, without using temperature data and age of the battery. The calculated ESR is then used to adjust the flash current. The process is repeated to correct for errors in the flash current.
In some prior proposals, since most of the factors that affect brown-out are not generally known to the user at the time of system operation (e.g., age of the battery; current temperature; size of the system load and flash load), a worst case voltage droop is assumed when a decision is made whether to activate the flash, if brown-out is to be avoided. However, assuming the worst case severely limits the usefulness of the flash (i.e., the flash won't trigger sometimes, even though the system could probably sustain a flash pulse) since the LED flash current drawn from the battery is calculated to be higher than it really is.
There is room for improvement in handheld electronic devices including a flash device and a battery.
There is also room for improvement in methods of driving a flash device of a handheld electronic device including a battery.
Similar numerals refer to similar parts throughout the specification.